Power supply with integrated linear high voltage multiplier and capacitors therefor

ABSTRACT

A high voltage power supply for use in small diameter spaces such as in oil well logging devices includes an AC voltage source which provides an AC voltage to a voltage multiplier circuit that converts the AC voltage to a high DC voltage. A parallel or combination parallel-series multiplication circuit is used, rather than a series multiplication circuit, to reduce the reverse voltage across each semiconductor rectifier in the multiplication circuit. A plurality of parallel capacitors is constructed using an elongate common capacitor electrode with individual capacitors formed from individual capacitor electrodes spaced along and separated from the common electrode by a layer of dielectric material. The layer of dielectric material can be tapered along the common electrode, and additional dielectric material can be positioned between edges of adjacent individual electrodes. A high voltage end individual electrode can be made wider to increase its capacitance.

RELATED APPLICATIONS

This is a continuation-in-part of application Ser. No. 12/397,015, filedMar. 3, 2009 now U.S. Pat. No. 8,203,858, entitled Power Supply withIntegrated Linear High Voltage Multiplier and Capacitors Therefor, nowU.S. Pat. No. 8,203,858, incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to power supplies for generatinghigh voltages. More particularly, the present invention relates to ahigh voltage power supply such as used with neutron generating tubes inoil well logging equipment. Further, the invention relates to anarrangement of special capacitors utilized in a linear fashion used inthese high voltage power supplies.

2. Related Art

Oil well logging devices which include neutron generating tubes are wellknown in the art. Such devices are sized to be lowered down an oil wellbore and emit neutrons into the formation through which the bore passes.By detecting the radiation coming back from the formation, particularlythe atoms in the formation that have been made radioactive by theemitted neutrons, the location of the oil bearing strata can bedetermined along the depth of the well. This indicates where the wellcasing should be perforated to allow oil to flow into the well.

The neutron generating tubes which are the heart of these loggingdevices require 100,000 volts or more to operate. Currently availablelogging devices generally use a Cockroft-Walton type voltage multipliercircuit which include capacitors and rectifiers, which takes an ACvoltage from a step up transformer and converts it to a high DC voltageby successively raising up the voltage in a step wise fashion to operatethe neutron generating tube. Voltage multiplying circuits usingcapacitors and rectifiers are well known, with the Cockroft-Waltonseries multiplier type circuit being commonly used in the currentlyavailable logging devices. These currently available logging devices cangenerally operate satisfactorily up to about 150 degrees C. Beyond thispoint, excessive electrical leakage in the semiconductors (rectifiers)preclude efficient power conversion. The leakage currents insemiconductors generally increase exponentially with increases intemperature. Many of the deep oil wells currently being drilled haveinternal temperatures in the deeper parts of the well over 150 degreesC. and up to 175 degrees C. or greater. This presents a problem inlogging the deeper portions of the wells because, as indicated, thepresently used logging devices do not operate satisfactorily at thesehigher temperatures.

In addition, in order to provide the required 100 kV of operatingvoltage required by neutron generating tubes, a reasonable limit must beimposed on the number of stages present in a Cockroft-Walton seriesvoltage multiplying circuit. Several reasons exist for this limit. Onedeals with the output voltage droop that occurs between no load and fullload conditions which is proportional to the cube of the number ofstages utilized. When the neutron tube is gated to be on, it is notuncommon to find the 100 kV dropping towards 80 kV as the power supplytries to feed into the load of the tube. A second problem that occurs isthe generation of ripple voltage that rides on the high voltage outputdue to the incomplete conversion of AC to DC voltage. This unwantedelectrical noise interferes with the acceleration voltage of the tubeand is difficult to remove from the process. Unfortunately, the ripplevoltage present on the high voltage output is proportional to the squareof the number of stages used in the multiplier.

There is currently a need for an oil well logging device that willoperate at temperatures above 150 degrees C.

SUMMARY OF THE INVENTION

It has been found that while semiconductor rectifiers operating at highreverse voltages, i.e., the rectifiers are used to block high voltages,break down or suffer excessive leakage currents at temperatures above150 degrees C., such rectifiers, if operated at lower voltages, willoperate satisfactorily up to and over 175 degrees C., the temperaturesneeded for operation in deep oil wells. Thus, if the voltages across therectifiers can be reduced, the operating temperature for the circuitsusing such rectifiers can be increased. By increasing the number ofstages used in a voltage multiplying circuit, the reverse voltage acrossthe rectifiers in each stage is reduced. However, as indicated above,the number of stages that can be included in the presently usedCockroft-Walton series multiplication circuits to provide the neededhigh output voltage without excessive output voltage droop and ripple isvery limited. Therefore, it is generally not possible to increase thenumber of stages in such Cockroft-Walton multiplier circuits above fivestages. It has been found that in voltage multiplier circuits utilizinga parallel or combination parallel and series multiplication scheme, thevoltage regulation (droop) and ripple does not scale as the cube andsquare of the number of stages used as it does in the Cockroft-Waltonseries multiplier circuits. In the parallel or combination parallel andseries multiplier circuit topology, the output voltage regulation(droop) scales only as the number of stages (N) while the ripple voltageis only a function of the capacitance used, independent of the number ofstages. Therefore, a much larger number of multiplying stages can beused to generate the needed high DC voltage output without seriousoutput voltage droop and ripple. If such voltage multiplying circuitscan be incorporated into oil well logging devices, such circuits can beused to provide the needed DC voltage to operate the neutron generatingtube at the higher temperatures above 150 degrees C. However, when usinga parallel or combination parallel and series voltage multipliercircuit, it is necessary to provide capacitors that will operate at highvoltages up to the output voltage of the power supply, usually at least100 kV. Providing high voltage capacitors that will physically fit intosuch circuits where the circuits have to fit into a cylindrical casewith an outside diameter between one and one half inch and two inches(75 mm diameters are common), is very difficult. Standard 100 kV disc ormica construction high voltage capacitors do not fit in such smalldiameter spaces.

According to the invention, a high voltage power supply which willoperate at high temperatures in excess of 150 degrees C. and which canfit into an oil well logging tool can be made by utilizing a voltagemultiplier circuit with a parallel or combination of parallel and seriesmultiplication schemes, so a much larger number of multiplying stages,for example, ten or twenty stages, can be used in the circuits therebyreducing the reverse voltage drop across each semiconductor rectifier.The lower reverse voltage drop across the rectifiers reduce the leakagecurrents thereby reducing the power loss, minimizing internal powerdissipation, and increasing system efficiency. This allows such circuitsto operate at higher temperatures. Since the voltage regulation andripple in such circuits does not scale as the cube and square of thenumber of stages used, better voltage regulation with less ripple isobtained. Because high voltage capacitors are required for suchcircuits, the invention uses a special novel construction of highvoltage capacitors that will fit into the small diameters required bythe oil well logging devices. By constructing the needed high voltagecapacitors from a common capacitor electrode, such as formed by anelongate piece of conductive material, for example a length ofcylindrical conductive material such as a length of metal tubing or rod,coated with a high voltage dielectric, such as several layers of aKapton or other plastic film material wrapped around at least a portionof the cylindrical length or a ceramic material positioned around atleast a portion of the cylindrical length such as a sleeve of aluminapositioned around the tube or rod, separate individual capacitorelectrodes can be formed on the dielectric with conductive material,such as with strips of conductive material wrapped concentrically withthe tube or rod outside the dielectric material. With this construction,a small diameter set of high voltage parallel capacitors can beconstructed to fit within an oil well logging device. To insuremechanical integrity, the entire apparatus may be encapsulated within ahigh voltage container by a high temperature potting material and placedwithin a metal outer case.

BRIEF DESCRIPTION OF THE DRAWINGS

Additional features and advantages of the invention will be apparentfrom the detailed description which follows, taken in conjunction withthe accompanying drawings, which together illustrate, by way of example,features of the invention, and wherein:

FIG. 1 is a general diagrammatic block diagram of an oil well loggingdevice as currently used to log oil wells, and with which the highvoltage power supply of the present invention may be used;

FIG. 2 is a vertical section through an oil well logging device ascurrently used again showing a general diagrammatic view of the loggingdevice of FIG. 1 and showing a four stage Cockroft-Walton high voltagemultiplier circuit;

FIG. 3 is a circuit diagram of a parallel embodiment of a voltagemultiplier circuit of the invention;

FIG. 4 is a generally schematic view of the physical arrangement of aparallel embodiment of a voltage multiplier circuit of the inventionimplementing the circuitry shown by the circuit diagram of FIG. 3 toform a ten stage negative output parallel multiplier circuit;

FIG. 5 is a vertical section through a capacitor of the invention takenon the line 5-5 of FIG. 4.

FIG. 6 is a vertical section similar to that of FIG. 5 with circuitcomponents slightly rearranged so that the circuit will fit into asmaller diameter space;

FIG. 7 is a circuit diagram of a combination parallel-series embodimentof a voltage multiplier circuit of the invention;

FIG. 8 is a generally schematic view of the physical arrangement of acombination parallel-series embodiment of the voltage multiplier circuitof the invention implementing the circuitry shown by the circuit diagramof FIG. 7 to form a ten stage negative output parallel-series multipliercircuit;

FIG. 9 is a vertical section through a capacitor of the invention takenon the line 9-9 of FIG. 8;

FIG. 10 is a vertical section similar to that of FIG. 9 with circuitcomponents slightly rearranged so that the circuit will fit into asmaller diameter space;

FIG. 11 is an assembly view of a different construction of the parallelcapacitor assembly of the invention;

FIG. 12 is a generally schematic view of the physical arrangement of aparallel embodiment of a voltage multiplier circuit of the invention asshown in FIG. 4, but showing a variation in the left end capacitors toincrease capacitance;

FIG. 13 is a fragmentary vertical section taken along the longitudinalaxis of a parallel capacitor construction of the invention showing analternate arrangement of individual capacitor electrodes;

FIG. 14 is a fragmentary vertical section similar to that of FIG. 13showing a further arrangement of individual capacitor electrodes; and

FIG. 15 is a fragmentary vertical section similar to that of FIG. 13showing an alternate arrangement of dielectric material between thecommon electrode and the individual capacitor electrodes.

Reference will now be made to the exemplary embodiments illustrated, andspecific language will be used herein to describe the same. It willnevertheless be understood that no limitation of the scope of theinvention is thereby intended.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

The invention is a high voltage power supply which can be used in anysituation where a high voltage power supply is needed. A specificapplication of the high voltage power supply of the invention is inconnection with oil well logging devices which are lowered down an oilwell while emitting pulses of neutrons into the formation through whichthe well extends to find the oil bearing strata intersected by the well.The specific example embodiments described herein are directed to thisspecific application, but the invention is not so limited.

Referring to FIGS. 1 and 2, an oil well logging device will generallyinclude a metal case 10 which houses a neutron source 12 in the form ofa commercially available neutron generating acceleration tube. Such atube requires a voltage of around 100,000 volts (100 kV) to acceleratecharged particles from a particle source to impact a target materialwhich releases neutrons when hit with the accelerated particles. Suchneutron sources are well known in the art and are commonly used in oilwell logging devices. The required high voltage for the neutron sourceis supplied by a high voltage DC power supply which usually includes anAC power source connected to a voltage multiplier circuit. In theillustrated embodiment of FIGS. 1 and 2, which represents a generalizedprior art oil well logging device, the AC voltage source is made up ofan AC power supply 14 connected to a step up transformer 16. As shown,the AC power supply is connected to the primary winding 15 of the stepup transformer 16, and the secondary winding 17 of the step uptransformer, which provides the AC output voltage signal of the AC powersource, is connected to the input of the voltage multiplier circuit 18.The voltage multiplier circuit 18 takes the AC output voltage signalfrom the AC power source, i.e., from secondary winding 17 of the step uptransformer 16, and converts it to the high voltage DC output 19 bysuccessively raising the voltage in a step wise fashion. The usualvoltage multiplier circuit 18 used in such currently available oil welllogging devices is a Cockroft-Walton series multiplier circuit as shownin FIG. 2. The high voltage DC output 19 of the voltage multipliercircuit 18 is connected in usual manner to the neutron source 12.

As indicated, the traditional logging devices as shown in FIG. 2generally include a cylindrical housing 10 which is suspended in an oilwell 22 by a cable 20 which can be extended from the top of the well tolower the logging device down the well or can be pulled up to raise thelogging device in the well. The well extends through a ground formation24 and may be cased with casing pipe 26. Because the casing of the wellis generally about two inches in inside diameter, the logging devicehousing has an outside diameter of less than two inches so that it canfit into and move up and down the well. This means that the insidediameter of the housing 10 for the device is between about one and onehalf and two inches. Everything in the housing as described has to fitwithin this small diameter.

As shown in FIG. 2, the AC power supply 14 may be a wire extending downthe cable 20 suspending the logging device from the top of the well. AnAC signal from the top of the well is then sent down the wire to thelogging device. Alternately, the AC power source can be located in thelogging device itself, and, for example, include a battery and aninverter to generate the AC input signal to the primary winding 15 ofthe step up transformer 16. A new drilling technique referred to as MWD(measure while drilling) uses well drilling equipment which incorporatesa well logging device with neutron generating tube in the drillingequipment. This means that the well is logged as it is drilled and thereis no separate logging device as shown in FIG. 2 that is lowered by acable into the well after the well is drilled. With this new drillingequipment, the various components described are incorporated into thedrilling equipment and operate in the same manner as described for theseparate logging device to perform the logging as the well is beingdrilled. With this new equipment, the AC power supply 14 may be a localgenerator which generates AC power as the drill rotates in the well.

FIG. 2 includes a circuit diagram for the traditional prior artCockroft-Walton series voltage multiplier circuit as the voltagemultiplier circuit of block 18. As shown in FIG. 2, a four stagetraditional Cockroft-Walton series multiplier circuit includes a set ofcapacitors 27 connected in series with the grounded output of the stepup transformer 16 and a set of capacitors 28 connected in series withthe ungrounded output of the step up transformer 16. The individualcapacitors of the two sets 27 and 28 of capacitors are connected by arectifier matrix made up of rectifiers 29. Each set of capacitors areshown with four individual capacitors connected in series with acorresponding capacitor of each series connected by two opposingpolarity rectifiers to form one of the four multiplication stages. Thus,the traditional Cockroft-Walton series multiplier circuit includes twosets of capacitors, each of which have the capacitors of the setconnected in series.

In the embodiments shown, the invention is directed to the voltagemultiplier circuit portion 18 of the high voltage power supply. Theother parts of the high voltage supply and the oil well logging devicein which the high voltage supply and the voltage multiplier circuit ofthe invention is shown, as an example of its use, generally remain thesame as for the prior art shown in FIGS. 1 and 2.

FIG. 3 shows a circuit diagram of a parallel embodiment of a voltagemultiplier circuit of the invention. This, rather than being atraditional Cockroft-Walton series multiplier circuit with two sets ofcapacitors connected in series, is a parallel multiplier circuit havingtwo sets of capacitors connected in parallel. A first set of capacitors30 made up of capacitors C1, C2, and C3 are connected in parallel to theoutput 31 of the secondary winding 17 of the step up transformer 16. Asecond set of capacitors 32 made up of capacitors C4, C5, and C6 areconnected in parallel with the grounded terminal 34 of the secondarywinding 17 of the step up transformer. The individual capacitors of thetwo sets 30 and 32 of capacitors are connected by a rectifier matrixmade up of rectifiers D1-D6. The rectifiers will generally besemiconductor rectifiers such as diodes. For ease of illustration, thecircuit of FIG. 3 shows only a three stage multiplier circuit withcapacitors C1 and C4 and rectifiers D1 and D2 making up the first stage,capacitors C2 and C5 and rectifiers D3 and D4 making up the secondstage, and capacitors C3 and C6 and rectifiers D5 and D6 making up thethird stage. As many stages as desired may be used, the more stagesbeing used, the less the voltage required to be blocked by any one ofthe rectifiers (the rectifier reverse voltage) for the same totalcircuit output voltage. In the parallel multiplier circuit topology, theoutput voltage droop (load regulation) is proportional only to thenumber of stages while the ripple voltage is only a function of thecapacitance used, independent of the number of stages. This is differentfrom the common Cockroft-Walton series multiplier circuits where thevoltage droop that occurs between no load and full load conditions isproportional to the cube of the number of stages utilized and the ripplevoltage present on the high voltage output is proportional to the squareof the number of stages used in the multiplier. Therefore, it isdesirable to limit the number of stages used in the prior artCockroft-Walton series multiplier circuits as much as possible. For oilwell logging equipment, it is common to use five stages in aCockroft-Walton multiplier circuit to provide the needed 100,000 voltoutput. The input voltage to such circuits provided by the step uptransformers are normally in the range of 20,000 volts. This produceslarge reverse voltage drops across the rectifiers used in theCockroft-Walton multiplier circuits which limit the performance of suchcircuits at high temperatures due to increased rectifier electricalleakage currents. For example, when the input to the Cockroft-Waltonseries multiplier circuit is 20,000 volts, the voltage required to beblocked by each of the rectifiers (the reverse voltage on therectifiers) is about 20,000 volts.

As indicated, because in the parallel multiplier circuit topology theoutput voltage droop (load regulation) is proportional only to thenumber of stages (as opposed to the cube of the number of stages) whilethe ripple voltage is only a function of the capacitance used,independent of the number of stages (as opposed to the square of thenumber of stages), when using parallel multiplier circuits as opposed tothe normally used Cockroft-Walton series multiplier circuits, the numberof stages can be increased significantly compared to the number ofstages used in the Cockroft-Walton series multiplier circuits.Therefore, to lessen the reverse voltage across the rectifiers tothereby increase the temperatures at which such circuits will operatesatisfactorily, the number of stages used in the parallel circuits, suchas the parallel circuit of FIG. 3, can be increased from the five stagesused in the series circuit to ten, twenty, or more in the parallelcircuits and, with the number of stages increased, the input voltagefrom the step up transformer to the multiplier circuit can be reduced.This also reduces the multiplication of the voltage at each stage of themultiplication circuit. For example, an input voltage of around 10,000volts can be used for a ten stage multiplier circuit (with 10,000 voltmultiplication for each stage) and an input voltage of around 5,000volts can be used for a twenty stage multiplier circuit (with 5,000 voltmultiplication for each stage) rather than the 20,000 volts for a fivestage Cockroft-Walton circuit (with 20,000 volt multiplication for eachstage). This reduces the reverse voltage across the rectifiers of about20,000 volts for the Cockroft-Walton series voltage multiplier circuitto about 10,000 volts for a ten stage parallel circuit and about 5,000volts for a twenty stage parallel circuit. However, parallel multipliercircuits require at least some capacitors operable at voltages equal toand near the output voltage of the voltage multiplier. Thus, while thevoltages across the rectifiers can be reduced with the use of morestages as allowed by the use of a parallel circuit, the voltage acrossthe capacitors is increased in such parallel circuits. This presents theproblem of providing high voltage capacitors that will fit into thesmall diameter spaces available in oil well logging equipment.

The use of the parallel multiplier circuits of the present invention inoil well logging equipment is possible with the use of a special highvoltage capacitor construction of the invention. FIG. 4 shows a physicalimplementation of the circuit of FIG. 3 using ten multiplier stages. Ascan be seen from FIG. 3, the parallel set 30 of capacitors C1 through C3which are connected in parallel all have a common connection of one sideof each capacitor to the secondary winding output 31 from the secondarywinding 17 of the step up transfer. This common connection makes itpossible to construct a set of capacitors all sharing a common capacitorelectrode or plate. Similarly, the parallel set 32 of capacitors C4through C6 which are connected in parallel all have a common connectionof one side of each capacitor to the secondary winding output 34 fromthe secondary winding 17 of the step up transfer. This common connectionmakes it possible to construct a second set of capacitors all sharinganother common capacitor electrode or plate. In the illustratedembodiment, the common capacitor electrode or plate for each set ofparallel capacitors 30 and 32 takes the form of a separate piece ofelongate conductive material, such as a piece of elongate tube or rod ofconductive material. The tube or rod as shown in FIGS. 4, 5, and 6 maytake the form of a brass tube 40.

Each common capacitor electrode 40 is coated with a dielectric material42 having a high breakdown voltage. It has been found that a wrapping ofmultiple layers of a polyimide film material such as KAPTON tape or filmmaterial around the common electrode, e.g., around the brass tube 40,provides a dielectric of sufficient breakdown voltage to be usedsatisfactorily in a 100,000 volt power supply. A single layer of theKAPTON film or tape, depending on the thickness, will withstand up toabout 30,000 volts. A wrapping of four layers of such KAPTON film ortape will withstand well over 100,000 volts. While the KAPTON film ortape has been found satisfactory for use in building the capacitors,various other electrically insulating materials can be used, such asTeflon or other plastics, ceramics, aluminum oxide, reconstructed mica,etc. With the dielectric layer around the common electrode, theindividual capacitors for a set of parallel capacitors can be easilyconstructed by forming individual electrodes of conductive material 44on the dielectric material, such as by wrapping a conductive material,such as a conductive foil material or a conductive band, around thedielectric 42. Each separate electrode formed by conductive material 44may be provided with a terminal connection 46 where the rectifiers 47and 48 are connected in opposite orientations to the individualcapacitor electrodes. Alternatively, the respective rectifiers can beattached, such as by soldering, directly to the conductive materialforming the individual electrodes without provision of specific terminalconfigurations. Care must be taken particularly with the last capacitortoward the output 49 of a tube 40 that the dielectric coating 42 extendsfar enough beyond the conductive material 44 forming the individualcapacitor electrode that there will be no arcing between the lastindividual capacitor electrode and the tube forming the commonelectrode. As shown, the dielectric material 42 can extend beyond theend of the tube 40 at the high voltage output end of a parallelcapacitor set. Also, although the difference in voltage between adjacentcapacitors is not high since the number of stages is large, theindividual capacitor electrodes 44 must be kept far enough apart alongthe tube to prevent arcing between the individual capacitors electrodes44. While shown as a cylindrical tube 40, the common capacitiveelectrode could take various other shapes and forms.

For a ten stage multiplier as shown in FIG. 4, which uses two sets often capacitors connected in parallel, the tubes 40 forming the commonelectrode of each set of the parallel capacitors can be about sevenmillimeters in diameter and about one hundred fifty millimeters inlength. The rectifiers 47 and 48 have tubular cases about fourmillimeters in diameter and about twenty five millimeters long. Therectifiers 47 and 48 are connected in opposite orientations betweenrespective sets of parallel capacitors formed by foil or bands 44 asshown in FIGS. 4-6 to form the circuit as shown in the circuit diagramof FIG. 3. The structure of FIGS. 4 and 5 can be bent into aconfiguration as shown in FIG. 6 so as to better fit into a space with adiameter as small as about thirty millimeters. This allows themultiplier circuit to be placed in oil well logging devices as shown inFIG. 6 showing the multiplier circuit inside of housing 10. Again, careneeds to be taken when positioning the tubes forming the capacitor setsclose together so that the tubes remain far enough apart that no arcingbetween capacitors will take place. Additionally, dielectric materialcan be placed between the respective tubes forming the parallelcapacitor sets or encapsulating dielectric material can be placedbetween and around the respective tubes forming the parallel capacitorsets to provide mechanical and electrical isolation between the commontube capacitors along the length of the multiplier. Alternately, thehousing 10 can be filled with a dielectric gas such as SF₆.

As apparent from the circuitry shown in FIG. 3, the parallel multipliercircuit includes a plurality of capacitors C4-C6 connected in parallelto ground and electrically connected to rectifiers D1-D6 being driven inparallel through parallel capacitors C1-C3 from the voltage source,i.e., output 31 of the step up transformer. Further, as seen from FIG.4, the parallel circuit configuration provides a plurality of stageshaving respective capacitors arranged linearly along the length of thecommon capacitor electrode, shown as tubes 40. The voltage increasesstage by stage which means with the illustrated physical construction,the step up voltage increases linearly with each stage and thereforewith respect to the physical spatial dimensions of the physical circuit.This means that the voltage between respective individual capacitorelectrodes 44 and the common electrode 40 increases successively fromone end (a low voltage end) to the opposite end (a high voltage end) ofthe common electrode.

FIG. 7 shows a circuit for a second embodiment of a voltage multipliercircuit of the invention. This, rather than being a traditionalCockroft-Walton series multiplier circuit, is a combinationparallel-series multiplier circuit. A set of parallel capacitors 50 madeup of capacitors C7, C8, C9, and C10 are connected in parallel to theoutput 31 of the secondary winding 17 of the step up transformer 16. Aset of series capacitors 52 made up of capacitors C11, C12, C13, and C14are connected in series, with one end of the series connected to thegrounded output 34 of the step up transformer 16 and the other end ofthe series forming the output 56 of the multiplier circuit. Theindividual capacitors of the two sets 50 and 52 of capacitors areconnected by a rectifier matrix made up of rectifiers D7-D14. Thecircuit of FIG. 7 shows a four stage multiplier circuit with capacitorsC7 and C11 and rectifiers D7 and D8 making up the first stage,capacitors C8 and C12 and rectifiers D9 and D10 making up the secondstage, capacitors C9 and C13 and rectifiers D11 and D12 making up thethird stage, and capacitors C10 and C14 and rectifiers D13 and D14making up the fourth stage. Similarly to the parallel multiplier circuittopology, with the combination parallel-series topology, the outputvoltage droop (load regulation) is proportional only to the number ofstages and the ripple voltage is only a function of the capacitanceused, independent of the number of stages. Therefore, as with theparallel circuitry described, with the parallel-series circuitry, thenumber of stages can be increased significantly compared to the numberof stages used in the Cockroft-Walton series multiplier circuits. Asmany stages as desired may be used, again, the more stages being used,the less the voltage required to be blocked by any one of the rectifiersfor the same circuit total output voltage.

With the parallel-series multiplier circuitry, again the voltage acrosseach of the rectifiers is reduced from that present in a standardCockroft-Walton series multiplier circuit so the multiplier circuitryworks well at high temperatures above 150 degrees C., but the parallelcapacitors have to be high voltage capacitors as almost the entireoutput voltage of the circuit appears across capacitor C10. FIG. 8 showsa physical implementation of the circuitry of FIG. 7 and shows a tenstage multiplier circuit. The parallel set 50 of parallel connectedcapacitors C7-C10 is constructed as a tube 60 with dielectric layer 62and individual capacitor electrodes 64 as described for FIG. 4.Rectifiers 66 and 68 are connected in opposite orientations betweenrespective individual capacitors of the sets 50 and 52 of capacitors toform the circuitry of FIG. 7.

With the circuitry of FIG. 7, the series capacitors C11-C14 do not havea common connection so individual capacitors 70, FIG. 8, are used. Noneof these capacitors have high voltage across them so do not have to bespecial high voltage capacitors. For example, using a ten stage circuitof FIG. 7, as shown in FIG. 8, the input from the step up transformedwill be about 10,000 volts peak to peak with the high voltage DC outputof about 100,000 volts. The voltage across each of the individualcapacitors C11-C14, FIGS. 7, and 70, FIG. 8, will be about 10,000 volts,while the voltage across the last of the parallel capacitors on the tube60 toward the output 56 will be close to about 100,000 volts. With thecircuit construction of FIG. 8, capacitors 70 can be standard ceramicdisc capacitors which have a diameter of about twenty millimeters and athickness of about eight millimeters. As indicated for FIG. 4, for a tenstage multiplier which uses ten capacitors connected in parallel, thetube 60 forming the common electrode of the parallel capacitors can beabout seven millimeters in diameter and about one hundred fiftymillimeters in length. The rectifiers 66 and 68 have tubular cases aboutfour millimeters in diameter and about twenty five millimeters long. Therectifiers 66 and 68 are connected in opposite orientations betweenrespective parallel capacitors formed by foil or bands 64 and respectiveindividual capacitors 70 as shown in FIGS. 8 and 9 to form the circuitas shown in the circuit diagram of FIG. 7. Again, this structure can bebent into a configuration as shown in FIG. 10 so as to better fit into aspace with a diameter as small as about thirty millimeters. This allowsthe multiplier circuit of FIGS. 7-9 to be placed in oil well loggingdevices as shown in FIG. 10 showing the multiplier circuit inside ofhousing 10. Again, dielectric material can be placed between and aroundthe respective components forming the parallel-series circuit to providemechanical and electrical isolation between the components along thelength of the multiplier. Alternately, the housing 10 can be filled witha dielectric gas such as SF₆.

As apparent from the circuitry shown in FIG. 7, the parallel-seriesmultiplier circuit includes a series of capacitors C11-C14 connectedelectrically in series and electrically connected to rectifiers D7-D14being driven in parallel through parallel capacitors C7-C10 from thevoltage source, i.e., output 31 of the step up transformer. Further, asseen from FIG. 8, the parallel-series circuit configuration provides aplurality of capacitors electrically connected in series from ground andin which the voltage increases at each individual capacitor of theplurality of capacitors connected in series, scaling linearly along aspatial length dimension of the series of capacitors, said seriescapacitors electrically connected to rectifiers being driven in parallelthrough parallel capacitors from the voltage source.

Either the parallel circuitry of FIGS. 3-6 or the parallel-seriescircuitry of FIG. 7-10 can be used to provide the high voltage DC neededto operate the neutron generating tubes, or other loads. The parallelversion of FIGS. 3-6 can be used when continuous output current is beingapplied to the neutron generating tube or other load. Theparallel-series version of FIGS. 7-10 is best suited for pulsed loadapplications such as where pulsed output current is applied to theneutron generating tube with the disc capacitors forming a chargestorage mechanism to supply the current during the large load pulses.

The AC power supply may provide an AC signal of various waveforms withvarious voltages. For Example, the AC power supply 14 may provide a 100Vpp sinusoidal AC signal to the input (primary winding 15) of the stepup transformer 16. With a ten stage multiplier circuit of the invention,the step up transformer may provide a ten kilovolt AC output to theinput of the voltage multiplier circuit 18. The voltage multipliercircuit then increases the voltage to a 100,000 volt DC output that isconnected to the neutron generator 12. With a twenty stage multipliercircuit of the invention, the step up transformer may provide a fivekilovolt output to the input of the voltage multiplier circuit 18. Thetwenty stage voltage multiplier circuit then, again, increases thevoltage to a 100,000 volt DC output that is connected to the neutrongenerator 12. Depending upon the output voltage needed, the availablevoltage supply, and the components used in the circuitry, variousvoltage supply signals can be used as input to the step up transformerand the step up transformer can provide various AC signals to themultiplier circuitry. Further, depending upon the AC voltage supplysignal available, a step up transformer may not be necessary. Ifappropriate, the AC voltage supply may alone be the AC voltage sourceand be connected directly to the voltage multiplier circuit.

An alternative construction for a parallel set of capacitors for eithera parallel or parallel-series voltage multiplier circuit is shown inFIG. 11. As shown in FIG. 11, rather than forming the dielectric layeron the common capacitor electrode such as by wrapping dielectric filmmaterial around the common electrode, the dielectric material, such as aceramic material, is formed into a separate sleeve 80 which can thentelescopically receive the elongate piece of conductive materialtherein. Thus, as shown in FIG. 11, the ceramic sleeve 80 is configuredto receive the elongate cylindrical common capacitor electrode 82therein. Thus, the sleeve 80 can be positioned over the common electrode82 or the common electrode 82 can be inserted into the sleeve 80. Thesleeve 80 may be open at both ends, or may be closed as at 84 at whatwill be the high voltage end 86. The closed end 84 provides additionalinsulation between the common electrode and the individual electrode 88at the high voltage end 86 of the sleeve to resist arcing between theindividual and common electrodes. This means that the closed sleeve enddoes not have to extend as far beyond the end of the common electrodereceived therein as does the film wrapping with open end as shown inFIGS. 4 and 8. The individual capacitor electrodes 88 can be formed onthe ceramic sleeve by metallization around the sleeve, such as by aprocess which metalizes the individual electrodes directly on theceramic sleeve, prior to insertion of the common electrode, or can beformed as previously indicated by conductive material being positionedaround or wrapped around the sleeve either prior to or after insertionof the common electrode.

It has been found that in many cases it is advantageous to provide ahigher capacitance value to the last capacitor at the high voltage endof the plurality of parallel capacitors constructed on the commoncapacitor electrode. This is particularly advantageous when the powersupply is used to supply power to a neutron tube or other device whichoperates in a pulsed mode. For example, a neutron tube or other devicemay operate in a pulsed mode where the device is on and drawing currentfrom the power supply for only intermittent periods. With a neutron tubewith a ten percent duty cycle, the tube is operated and draws currentfrom the output of the high voltage power supply (the output of thevoltage multiplier circuit) only ten percent of the time. This meansthat the actual current drawn by the neutron tube during the time thatit is drawing current is ten times the average current draw. For suchpulsed operation, it is important to have as much capacitance aspractical charged up to the output DC voltage of the voltage multipliercircuit, such as to the example 100 kV output voltage, at the start ofoperation of the neutron tube. This can be done by increasing thecapacitance of the last two capacitors (the last capacitor of eachplurality of capacitors), both of which are charged to substantially theoutput potential of the voltage multiplier circuit. Therefore, the lastcapacitor and usually the next to last capacitor will supply the currentto the device during its operation. With a ten percent duty cycle, thecapacitors will supply current to the device ten percent of the time andtherefore can discharge power into the device this ten percent of thetime and will have ninety percent of the time to recharge. Thisincreases the power that can be applied to the device during itsoperation to improve performance of the device. For the plurality ofcapacitors connected in parallel using the common electrode constructionof the invention, the capacitance of the last capacitor can be increasedby making the last individual electrode of the parallel capacitors widerwhich means that more charge is built up on this last individualelectrode. With a high voltage output of 100 kV, more of this 100 kVcharge is built up on this wider electrode and this increased charge isavailable to run the device.

FIG. 12 shows an embodiment of a parallel multiplier circuitconstruction of the invention similar to that of FIG. 4, but with thelast capacitor on the high voltage end of each common capacitorelectrode having an increased capacitance. This increased capacitance isprovided by making the last individual capacitor electrode, shown aselectrode 98 on the right end of each of the common electrodes 40, widerthan the other individual electrodes 44. These wider individualelectrodes 98 provide increased capacitance compared to the narrowerindividual electrodes 44. Typical values of capacitance of thecapacitors formed by the narrower electrodes 44 of a typical examplemultiplier of the invention are about 10 pF. By increasing the length ofthe individual electrodes 98 of last two capacitors, capacitance ofthose capacitors can be effectively increased up to about 50 pF. Thismeans that with a ten percent duty cycle, the dynamic output voltagedroop of the voltage multiplier circuit is reduced by a factor of aboutten. Typical example individual narrower capacitor electrode widths(electrodes 44) are about 0.75 inches whereas the increased width of thelast capacitor electrodes (electrodes 98) can be up to three to fourinches.

With the combination parallel-series voltage multiplier circuit of FIG.8, the capacitance of the last capacitor of the plurality of capacitorsconnected in parallel on the common electrode (the next to lastcapacitor for the high voltage output of that circuit) can similarlyhave its capacitance increased by making its individual electrode widerthan the other individual electrodes. The capacitance of the lastcapacitor at the high voltage output end of that circuit, i.e., the lastcapacitor of the plurality of capacitors 70 connected in series, isincreased by providing an individual capacitor 70 of increasedcapacitance.

In the example use of the multiplier circuit of the invention in oilwell logging devices, the length available in such devices for thecommon electrode capacitor construction is generally limited, whichlimits the width of each individual capacitor electrode that can beused. The lengths usable in most currently used oil well logging devicesare about thirty inches to forty-two inches. Longer lengths can be usedin specially built devices, with a length of about sixty inches usablein one custom built prototype device requiring more power from thevoltage multiplier circuit than necessary for most such devices. Withlimited length available, in order to maximize the number voltagemultiplication stages used and to maximize the capacitance of eachcapacitor used, in most cases it is necessary to minimize the spacebetween each of the individual capacitor electrodes along the allowedlength of the common electrode. The example embodiments illustrated sofar show the individual capacitor electrodes (electrodes 44 in FIG. 4and electrodes 64 in FIG. 8) spaced along the dielectric layer aroundthe common electrodes (dielectric layers 42 and common electrodes 40 inFIG. 4 and dielectric layer 62 and common electrode 60 in FIG. 8) withrelatively large separation between such electrodes. This largeseparation shown is principally for illustration purposes. However, aspreviously mentioned, precautions have to be taken to prevent arcingbetween adjacent electrodes and with the example construction shown inFIGS. 4 and 8, the electrodes have to be spaced far enough apart toprevent arcing between adjacent electrodes. With the circuitconstructions shown, the voltage between adjacent capacitor electrodesis reduced with an increase in voltage multiplier stages. Therefore, thespacing between electrodes can be reduced as the number of stages isincreased. However, in many cases, such as depending upon the number ofmultiplication stages desired, the output voltage desired, and thelength of the common electrode available, maintaining sufficient spacebetween the individual electrodes is difficult.

FIG. 13 show an embodiment of the parallel capacitor constructionallowing closer spacing of adjacent individual electrodes. As shown, thebasic construction of the plurality of parallel capacitors is the sameas shown in FIGS. 4 and 8 with a conductive elongate tube or rod 100forming the common electrode which is surrounded with a high breakdowndielectric material 102. The individual capacitor electrodes 104 areformed around the dielectric material 102 in any suitable manner, suchas by wrapping a conductive material or depositing a conductive materialaround the dielectric material 102. However, as shown in FIG. 13,additional dielectric material 106, such as a dielectric material tapeor film such as a polyimide or Teflon tape or film, is positioned toextend between the edges of adjacent individual electrodes 104. Whilethe additional dielectric material 106 is shown extending fully undereach of the individual electrodes 104, it is only necessary that itextend far enough under the edge of one electrode and over the top ofthe adjacent electrode far enough to prevent arcing between adjacentelectrodes around the additional dielectric material 106. Further, sincethe voltage difference between adjacent individual electrodes is not asgreat as the voltage difference between most of the individualelectrodes and the common electrode, the additional dielectric material106 does not need to be as thick as the layer of dielectric material 102surrounding the common electrode 100 separating the individualelectrodes 104 from the common electrode 100. In most cases, a singlelayer of dielectric tape or film can be used for the additionaldielectric material 106 between the edges of the individual electrodes.This additional dielectric material 106 between adjacent edges of theindividual electrodes 104 allows the individual electrodes 104 to bespaced much closer together in almost abutting relationship. With thedielectric tape or film extending under one electrode and over the topof the adjacent electrode, this tape usually will need to be applied asthe individual electrodes are being formed around the dielectricmaterial layer 102 surrounding the common electrode 100.

FIG. 14 shows a further embodiment for reducing the space betweenadjacent individual electrodes along the common electrode. Again, thebasic construction of the plurality of parallel capacitors is the sameas shown in FIGS. 4 and 8 with a conductive elongate tube or rod 110forming the common electrode which is surrounded with a high breakdowndielectric material 112. The individual capacitor electrodes 114 areformed around the dielectric material 112 in any suitable manner, suchas by wrapping a conductive material or depositing a conductive materialaround the dielectric material 112. In the embodiment of FIG. 14, theindividual capacitor electrodes 114 are divided into two sets ofalternating individual capacitor electrodes, a first set made up ofcapacitor electrodes 114 a and a second set made up of capacitorelectrodes 114 b. By alternating capacitor electrodes is meant that oneset of electrodes starts with an end capacitor electrode, skips the nextelectrode, includes the next electrode, skips the next electrode, andcontinues in such manner so as to include every other electrode startingfrom the first electrode in the set. The second set starts with thecapacitor electrode adjacent the first electrode of the first set andincludes every other electrode thereafter. Thus, each capacitorelectrode of the second set would be an electrode immediately adjacentat least one of the electrodes of the first set, i.e., the electrodes ofeach set alternate along the length of the common capacitor electrodewith the electrodes of the other set as indicated by capacitorelectrodes 114 a and 114 b in FIG. 14.

As shown in the embodiment of FIG. 14, the alternating individualcapacitor electrodes 114 a of the first set are positioned againstdielectric material 112 surrounding common electrode 110. Thesealternating individual electrodes 114 a are spaced apart approximatelythe width of the individual electrodes 114 or somewhat less than thewidth of the electrodes 114. Additional dielectric material 116, such asa dielectric material tape or film such as a polyimide or Teflon tape orfilm, is positioned to extend over and between the adjacent edges ofadjacent individual electrodes 114 a of the first set. The second set ofalternating electrodes 114 b are then formed on top of the additionaldielectric material 116 so as to extend between and to or over the edgesof adjacent individual electrodes 114 a and cover the space betweenadjacent electrodes 114 a of the first set. When the electrodes 114 bextend to the edges of adjacent individual electrodes 114 a over thespace between the adjacent edges, the entire length of the commonelectrode is surrounded by individual electrodes and the electrodes forma parallel connection of all of the individual electrodes 114. When thespace between adjacent individual electrodes 114 a is smaller than thewidth of the individual electrodes 114, the edges of adjacent individualelectrodes 114 b extend over the edges of adjacent individual electrodes114 a so that the edges of electrodes 114 b overlap the edges ofelectrodes 114 a. In such instance, a hybrid between series and parallelcapacitors would be formed along the common electrode with the degree ofseries capacitance depending upon the degree of overlap. Again, sincethe voltage difference between adjacent individual electrodes is not asgreat as the voltage difference between most of the individualelectrodes and the common electrode, the additional dielectric material116 does not need to be as thick as the layer of dielectric material 112surrounding the common electrode 110 separating the individualelectrodes 114 from the common electrode 110. In most cases, a singlelayer of dielectric tape or film can be used for the additionaldielectric material 116 between the edges of the individual electrodes.While the additional dielectric material 116 is shown extendingcompletely over the space between adjacent electrodes 114 a of the firstset, such additional dielectric material need only extend far enoughfrom an edge of an electrode 114 a of the first set to prevent archingbetween respective capacitor electrodes 114 a of the first set andadjacent capacitor electrodes 114 b of the second set.

In some cases it may be advantageous to maximize the capacitance of eachof the individual capacitors along the common capacitor electrode. Thismay be to provide capacitors of different capacitance or to allowvarying widths of individual capacitor electrodes to differ while stillproviding substantially the same capacitances value. The capacitancevalue of an individual capacitor along the common capacitor electrodewill depend upon the voltage across the capacitor and the thickness ofthe dielectric. Lower voltage capacitors can use a thinner dielectricwhich raises the capacitance of the lower voltage capacitors for thesame width of individual capacitor electrode. Since the voltage acrossthe individual capacitors increases along the length of the commonelectrode, and since a thinner dielectric can be used in the lowervoltage capacitors, it is possible to taper the thickness of thedielectric layer surrounding the common electrode from the low voltageend to the high voltage output end. FIG. 15 shows an embodiment of theparallel capacitor construction wherein the dielectric layer 122 betweenthe common electrode 120 and the individual capacitor electrodes 124 istapered to increase in thickness as it extends from the lower voltageend of the parallel capacitor circuit, the left end in FIG. 15, towardthe high voltage output end, the right end in FIG. 15. Where thedielectric layer 122 is formed by winding a dielectric tape or filmmaterial around the common electrode 120, the dielectric layer may betapered in stepwise fashion, as shown, with the thicker steps formed byadditional windings of the dielectric tape or film material. Thesethicker steps may be formed for each of the individual electrodes 124,or several individual electrodes may be formed on each of the steps.Where a ceramic or other type of material is formed around the commonelectrode to form the dielectric layer 122, or where a sleeve ofdielectric material as shown in FIG. 11 is used, a continuous smoothtaper may be used.

While the invention has been illustrated and described with respect toembodiments of the invention specifically designed for use in oil welllogging applications, it should be realized that the invention can beused in any application where any high voltage DC is required. Further,with the arrangement of the rectifiers in the circuits as shown in thedrawings, the high voltage DC output is a negative voltage which isneeded for the neutron generating tubes. If used in a differentapplication where a positive high voltage DC is needed, the polarity ofthe respective rectifiers is reversed.

With the parallel and parallel-series circuits for the voltagemultiplier of the invention, the capacitors are the components of thecircuit across which the higher voltages appear. The reverse voltageacross the rectifiers is reduced over the reverse voltages that appearin a series circuit because many more stages may be used without havingthe problem of the N (number of stages) cubed droop problem or N squaredripple problems. This lower reverse voltage allows the highertemperature operation of the circuits. With such parallel andparallel-series circuits, the voltage across a plurality of thecapacitors in the circuit is greater than the voltage across any one ofthe rectifiers in the circuit. Further, the entire output voltage willgenerally appear across one of the capacitors. Further, with thephysical construction of sets of parallel capacitors along a commoncapacitor electrode where the common electrode is elongate, and with theindividual capacitors arranged along the length of the common electrode,the stepped up voltages will appear on consecutive capacitors so thatthe stepped up voltages will increase linearly with respect to thephysical spatial dimensions of the circuits. Further, with theparallel-series combination circuit, the series connection of thecapacitors will provide a voltage increase across each individualcapacitor which scales linearly along the spatial length dimension ofthe circuit.

While the forgoing examples are illustrative of the principles of thepresent invention in one or more particular applications, it will beapparent to those of ordinary skill in the art that numerousmodifications in form, usage and details of implementation can be madewithout the exercise of inventive faculty, and without departing fromthe principles and concepts of the invention. Accordingly, it is notintended that the invention be limited, except as by the claims setforth below.

The invention claimed is:
 1. A voltage multiplier circuit comprising: anAC input terminal and a ground terminal between which an AC power sourceis connected to provide an AC input of desired voltage to the voltagemultiplier circuit; a DC output terminal to provide a DC output voltagebetween the DC output terminal and the ground terminal greater than theAC input voltage; a plurality of rectifiers connected in series having afirst rectifier of the series connected to the ground terminal and alast rectifier of the series connected to the DC output terminal; afirst plurality of capacitors electrically connected in parallel to theAC input terminal and to the plurality of rectifiers; each of the firstplurality of capacitors having at least one terminal electricallyconnected to the AC input terminal and a second plurality of capacitorselectrically connected to the plurality of rectifiers, each rectifier ofthe plurality of rectifiers connecting a capacitor of the firstplurality of capacitors to a capacitor of the second plurality ofcapacitors.
 2. A voltage multiplier circuit according to claim 1,wherein the second plurality of capacitors are electrically connected inparallel to the ground terminal.
 3. A voltage multiplier circuitaccording to claim 2, wherein the total output voltage of the highvoltage power supply appears across one of the capacitors of the secondplurality of capacitors.
 4. A voltage multiplier circuit according toclaim 1, wherein the second plurality of capacitors is connected inseries having a first capacitor of the series connected to the groundterminal and a last capacitor of the series connected to the DC outputterminal.
 5. A voltage multiplier circuit comprising: an AC inputterminal and a ground terminal between which an AC power source isconnected to provide an AC input of desired voltage to the voltagemultiplier circuit; a DC output terminal to provide a DC output voltagebetween the DC output terminal and the ground terminal greater than theAC input voltage; a plurality of rectifiers connected in series having afirst rectifier of the series connected to the ground terminal and alast rectifier of the series connected to the DC output terminal; afirst plurality of capacitors electrically connected in parallel to theAC input terminal and to the plurality of rectifiers; and a secondplurality of capacitors electrically connected to the plurality ofrectifiers, each rectifier of the plurality of rectifiers connecting acapacitor of the first plurality of capacitors to a capacitor of thesecond plurality of capacitors; wherein the first plurality ofcapacitors electrically connected in parallel are constructed with acommon capacitor electrode, a plurality of individual capacitorelectrodes, and dielectric material positioned between each individualcapacitor electrode and the common electrode, and wherein the commoncapacitor electrode is connected to the AC input terminal.
 6. A voltagemultiplier circuit according to claim 5, wherein the common capacitorelectrode is elongate with opposite ends, the plurality of individualcapacitor electrodes are spaced along the elongate common electrodebetween the opposite ends, and the voltage between respective individualelectrodes and the common electrode increases successively from a lowvoltage end of the common electrode to a high voltage end of the commonelectrode, and the individual capacitor electrode closest the highvoltage end is wider than the other individual capacitor electrodesalong the common electrode.
 7. A voltage multiplier circuit according toclaim 5, wherein the common capacitor electrode is elongate withopposite ends, the plurality of individual capacitor electrodes arespaced along the elongate common electrode between the opposite ends,and the voltage between respective individual electrodes and the commonelectrodes increases successively from a low voltage end of the commonelectrode to a high voltage end of the common electrode, and thedielectric material positioned between each individual capacitorelectrode and the common electrode increases in thickness from the lowvoltage end to the high voltage end of the common electrode.
 8. Avoltage multiplier circuit according to claim 5, including additionaldielectric material extending between edges of adjacent individualcapacitor electrodes.
 9. A voltage multiplier circuit according to claim8, wherein the additional dielectric material extending between theedges of adjacent individual capacitor electrodes includes a dielectrictape or sheet material extending from underneath one individualcapacitor electrode over the top of an adjacent individual capacitorelectrode thereby positioning the additional dielectric material betweenthe edges of the adjacent individual capacitor electrodes.
 10. A voltagemultiplier circuit according to claim 5, wherein the individualcapacitor electrodes are divided into a first and a second set ofalternating adjacent individual capacitor electrodes, the individualcapacitor electrodes of the first set being separated from the commonelectrode by the dielectric material and spaced apart along the commonelectrode no more than approximately the width of the individualcapacitor electrodes of the second set, and including additionaldielectric material positioned over and between edges of adjacentindividual capacitor electrodes of the first set, wherein the individualcapacitor electrodes of the second set are positioned over theadditional dielectric material which separates the individual capacitorelectrodes of the second set from the individual capacitor electrodes ofthe first set.
 11. A voltage multiplier circuit according to claim 5,wherein the individual capacitor electrodes are divided into a first anda second set of alternating adjacent individual capacitor electrodes,the individual capacitor electrodes of the first set being separatedfrom the common electrode by the dielectric material and spaced apartalong the common electrode no more than approximately the width of theindividual capacitor electrodes of the second set, the individualcapacitor electrodes of the second set extending between adjacentindividual capacitor electrodes of the first set, and includingadditional dielectric material positioned between individual capacitorelectrodes of the first set and the second set.
 12. A voltage multipliercircuit according to claim 5, wherein the second plurality of capacitorsare electrically connected in parallel to the ground terminal andwherein the second plurality of capacitors electrically connected inparallel are constructed with a common capacitor electrode, a pluralityof individual capacitor electrodes, and dielectric material positionedbetween each individual capacitor electrode and the common electrode,and wherein the common capacitor electrode is connected to the groundterminal.
 13. A voltage multiplier circuit according to claim 5,wherein, for each plurality of capacitors electrically connected inparallel, the common capacitor electrode is elongate with opposite ends,the plurality of individual capacitor electrodes are spaced along theelongate common electrode between the opposite ends, and the voltagebetween respective individual electrodes and the common electrodeincreases successively from a low voltage end of the common electrode toa high voltage end of the common electrode, and the individual capacitorelectrode closest the high voltage end is wider than the otherindividual capacitor electrodes along the common electrode.